The mammalian kidney is used as a model to study the genetic basis of development and oncogenesis in a complex multicellular tissue. Current studies continue to focus on the role of transcription factors in early kidney development and their regulation by potential tumor suppressor genes. The objectives are to understand how developmental regulatory genes can contribute to oncogenic transformation. A. Development. The Pax-2 gene is activated early after kidney induction, in mesenchymal cells destined to become the renal epithelium. Using in vitro embryonic kidney cultures and antisense oligonucleotides against the Pax-2 gene, we have shown a clear requirement for this transcription factor in the transition of the kidney mesenchyme to epithelium. Furthermore, the requirement for Pax-2 is transient, as the terminally differentiating proximal and distal epithelial cells suppress Pax-2 expression. Persistent expression of Pax-2 in transgenic mice results in severe kidney abnormalities similar to human congenital nephrotic syndrome. B. Oncogenesis. The suppression of Pax-2 during kidney development is mediated, in part, by the Wilms' tumor suppressor gene, WT1. There is a direct correlation between decreasing levels of Pax-2 protein and increasing levels of WT1 in the developing nephron. Furthermore, WT1 binds at least three sites in the Pax-2 5' regulatory sequences and can repress transcription in vitro. Pax-2 is expressed in Wilms' tumor, an embryonic tumor derived from mesenchymal blastema or undifferentiated epithelium. Pax-2 expression can also be detected in renal cell carcinoma from adult patients. This may be due to reactivation of Pax- 2, or hyperproliferation of a renal stem cell population that has never repressed the Pax-2 gene. in any event, cell lines derived from renal cell carcinomas can be growth inhibited with Pax-2 antisense oligonucleotides, suggesting that activation of Pax-2 is a necessary determinant for oncogenesis. C. Biochemistry. In order to understand the function of the Pax family of transcription factors, identifying the potential target genes is mandatory. using Pax-2 specific antibodies, DNA-protein complexes were precipitated from intact chromatin and the DNA binding sequences cloned. DNA footprinting and methylation protection experiments clearly demonstrate Pax-2 binding to these genomic loci. These genomic tags can be used to identify larger genomic clones that may contain potential target genes.